Computer to plate (CTP) – The procedure is a concept, photopolymer properties alter under exposure to UV light. A similar technology is present in the coating on aluminium lithographic printing plates, both are exposed to UV light through a digital movie (positive or negative) and in the circumstances of’ positive’ litho plates the uncovered area is flushed away but in correct of photopolymer the unexposed material is washed away while the totally exposed part is hardened, thus film negatives are used.
Photopolymer is available in a wide variety of forms and offset ctp platesetter with various characteristics, the principle feature for letterpress is the’ shore hardness’ that could range from low 20 ‘s to around eighty five beyond doubt steel backed plates, the harder plates (sixty upwards) being perfect for much deeper impression work. There are certain problems to keep in mind – each and every component of the processing cycle is vital and any variable is important. Each plate type according to it’s very own specification will require various exposure times, washout times & temperatures, oven temperatures for drying as well as drying times and post exposure. It appears difficult but it’s surprisingly straight forward.
A film negative features the preferred image or design being printed or’ letterpressed’. A portion of photopolymer plate is lower corresponding to the picture size and then placed in the exposure tray. The film negative is overlayed seeing to it the film (emulsion side down) is in contact that is good with no air bubbles or perhaps sections between the movie and plate that’ll cause UV leakage and a blurred image. The vacuum blanket is rolled over the movie and plate, drawer closed plus the exposure time begins beginning the vacuum and UV lighting.
After exposure the plate is put into the washout product for a number of minutes (depending on plate type) in water around 20c. Soft brushes rotate to cleanse away waste material and the plate is right away dehydrated to get rid of extra water and positioned in the drying unit for the appropriate time at a temperature between 60c and 80c. After initial drying is complete plates are post exposed to UV light without the vacuum (as no film is required only at that point) and also placed once more in to the hair dryer, the next drying time is important to make certain the plates are properly’ detacked’.
he plate is today done and can be mounted on double sided adhesive ready to place on a precision ground metal platform on the press, the entire operation taking around 30 – 40 minutes. For letterpress the preferred plates are’ foil’ (meaning plastic) backed instead steel backed that are hard to cut and work with, particularly for multi colour work. Of the foil backed plates available the KF range by Toyobo is one of the most widely used and popular and particularly the KF95 (0.95mm plate) and the KF152 (1.52mm plate). It has to be remembered that the deeper plates just like the KF152 need more length of exposure so the UV is able to penetrate to the floor belonging to the plate and correctly cure or perhaps harden the polymer.
Failing to perform this could lead to weak plates which do not survive the print run with good details slowly disappearing from the inked impression. The plate should then be loaded behind to compensate but this’s problematic and not desirable. Even during well made plates you will discover limits towards the level of fine detail achievable in uv ctp lasers, lines below 0.3 pt could very well not hold through the production system.
Important improvements in technology have created the polymer plate system even more feasible in recent years at both entry level and also for big lithographic businesses both experiencing advancements towards a more’ computer to plate’ (CTP) process. In lithography this is a slightly different process by using a variation of the photopolymer plate application referred to as Flexography which focuses more on accurate halftones needed by modern presses. For both Flexography and Photopolymer for Letterpress, CTP is actually forwarded by the advancement of brand-new polyester based films.
Developments in laser films do not seem to be effective because of this kind of top quality work but inkjet films achieve consistent industry standard results with DMAX > 4 although it’s necessary to work with a software RIP to achieve this. The good results of the polyester films lies in the greater accuracy of modern inkjet printers (the minimum requirement will be an anhubg including the Epson 4900 which is still a relatively modest investment) as well as in the science on the film product.
We have tested a wide variety but endorse the Folex product Reprojet P Hd on 30 meter rolls or trim sheets. The film runs not by holding enough ink being a dense black and so get to the DMAX target but by the filament inside of the structure of the movie working with the ink to deflect light and cut it away on the polymer. We have discovered in testing that exposure times greater than needed could lead to UV leakage (particularly if the ink is just too light) but then plate makers must be working hard to the manual times specified by plate manufacturers so this is not a concern.
The movie is going to hold an amazing amount of ink which combined with the film ‘s properties provide excellent results. Trying to print movie that has no RIP like Waasatch, Efi or Filmgate simply using the ctcp machine will result in floating (ink literally drifting on the surface) and wastage. These RIP’s are and added expense to small print stores but there’s a less expensive option in Accurip which we’ve tested running at droplet size 13 out of fifteen and the outcomes are superb. We have additionally used EFI and are intending to test Waasatch. Any of these RIP’s perform the important task of taking control of the way ink is laid down and also the total amount whereas onboard printer drivers will set up the ink down, in terms which are simple, too much too quickly.
With the resurging interest in letterpress and especially the artform side of this printing process, photpolymer plates have been in increasing demand in the Uk and in specific plates that permit a much deeper opinion in to thick paper with the luxury stationery market. Though polymer plates are already available for a while the KF152 for great impression work hasn’t been sent out in the Uk in recent times. There’s now a distributor and Lyme Bay Press are providing KF152 plates as the single distributor and a plate making system as well as tech support team for all those with printing problems, encouraging brand new development in the letterpress community.